In computed radiography, which technology may be used in place of the photomultiplier tube (PMT) in the image reader system?

• A. Thin-film transistor (TFT)
• B. Amorphous selenium (a-Se)
• C. Charge-coupled device (CCD)
• D. Analog-to-digital converter (ADC)

Answer: (C)

In computed radiography, the image reader’s job is to detect the light emitted from the phosphor as the plate is scanned, turning that light into an electrical signal. A photomultiplier tube was the traditional detector for this light, but a charge-coupled device can take its place because it directly converts incoming photons into an electrical signal with high sensitivity and good spatial sampling. This solid-state option fits well with the scanning geometry of the reader and provides reliable, fast readout.

The other options don’t function as the light-detecting element in the CR reader. A thin-film transistor array is typically used with flat-panel detectors rather than the CR readout chain. Amorphous selenium is a photoconductor used in direct digital radiography to convert X-rays to charge, not to detect the readout light. An analog-to-digital converter digitizes the signal after detection, so it isn’t the device that converts light to an electrical signal.